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Advance from RPM max question

I noticed that in a tune that I have that is NOT a turbonator tune, advance from rpm max graph line starts out at low rpm with high advance, for example 900 rpm might be at 54 degrees and 7000 rpm might be 39 degrees with advance decreasing as rpm increases. In turbonator tunes timing goes in the opposite direction, 900 rpm would be 28 degrees 5000 rpm might be 49 degree's. Can someone explain this?

The only substitute for cubic inches is cubic dollars, how fast can you afford to go?

Re: Advance from RPM max question

Brian, that is a surprise, that would never have occurred to me. In the knowledge center, shelgame talks about total timing being calculated by adding basic timing + advance from RPM + Advance from map. He then later says there is no such thing as basic timing. That causes me to ask which of the formula's below would give the correct answer to your total timing at any given point. I am using representative numbers.
basic timing = 12 degrees + advance from rpms 30 degrees + Advance from map -20 degrees. 12 + 30 + -20 = + 22 degree total advance, OR...
basic timing = 0 degrees + advance from rpms 30 degrees + Advance from map -20 degrees. 0 + 30 + -20 = + 10 degrees total advance

Last edited by jeff1234; 07-05-2019 at 11:59 PM.

The only substitute for cubic inches is cubic dollars, how fast can you afford to go?

Re: Advance from RPM max question

IIRC,Shelgame was trying to get the reader to understand that there is no base timing. We do not have a crank sensor so the ECU does not know where TDC is. All it knows is the position of the dizzy, and the cutout in one of the flags identifies which cylinder is which via the HEPs. All timing are relative to the position of the distributor, this position maybe or may not be 12 BTDC.

A  There is no such thing as base timing. Total timing is pretty simple  Advance from RPM + Advance from MAP is the basic timing. The advance from MAP can be either the WOT or P/T table depending on TPS position. And, there is a WOT multiplier for the advance from MAP table for when the lookup value from that table is negative. There is also a maximum timing value.

Q - So I am clear on this.... The timing shown in the cal, and on a Scan Tool, will be the total timing. This number assumes the base timing of 12* (or whatever is called for on the emissions label) is there. So the number shown in a cal is not necessarily the number used in a calculation, correct?

A - There is no such thing as base timing. The 12* is just the fixed timing used to set the sync between the distributor and the crank. The reason they chose 12* is simply because an engine generally will not run well @ 0* advance. The 12* is not a 'base' timing at all. It's simply a reference point. It never gets 'added' to anything. All the timing figures in the cal are relative to TDC (0*).

If the sync is in fact wrong (ie, you set the sync at 14* instead of 12*), then the actual timing will be off by the same amount (2* in this example). But, the ECU will not know about that difference and will not be able to report it to a scan tool.

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